1. Field of the Invention
The invention relates to pen-based data input systems and, more particularly, to an improved writing device for data entry into a pen-based data input system.
2. Description of the Background Art
A personal digital assistant (PDA) typically utilizes a writing "pen" for entering data using a so-called pressure sensitive liquid crystal display (LCD) screen. Generally, the LCD has a transparent pressure sensitive overlay that is used to detect the position of a pen stylus relative to the screen, e.g., using a piezo-electric or resistive technique. The screen typically has a deformable plastic faceplate against which a stylus tip of the pen is pressed to "write" on the screen. As the stylus position is detected, the PDA illuminates a pixel or pixels on the underlying LCD. Consequently, as the stylus is moved, an image appears on the LCD which tracks the stylus position.
A microprocessor stores the image in memory as a bit map, or otherwise processes the image, e.g., character recognition. Besides PDA's, this form of data input device is also used by graphic artists in so-called drafting/drawing tablets.
The pen typically contains a body which is grasped by the user and a Teflon.RTM. stylus (or tip) that impacts the screen. Teflon.RTM. is a registered trademark of E. I. DuPont de Nemours, Co. The stylus is typically made of Teflon.RTM. to promote a smooth writing action and to reduce friction as well as damage to the screen.
However, those skilled in the art have recognized that the Teflon.RTM. stylus does, over time, scratch, mar and otherwise degrade the screen. In fact, after heavy use, the screen may be degraded to a point where it becomes useless. To combat such degradation, disposable plastic overlays have become available to protect the screen. However, such overlays degrade the position detection accuracy.
Therefore, there is a need in the art for an improved writing device for entering information into a pen-based input system used in a PDA or drafting/drawing tablet.